Fermentation of organic wastes and CO2 + H2 off-gas by microbiotas provides short-chain fatty acids and ethanol for n-caproate production. Issue 42 (December 2020)

• Record Type: Journal Article
• Authors: González-Tenorio, Diana; Muñoz-Páez, Karla M.; Buitrón, Germán; Valdez-Vazquez, Idania
• Is Part Of: Journal of CO₂ utilization. Issue 42(2020)
• Publication Date: 2020-12
• Subjects: acetogens -- biogenic CO2 -- biorefineries -- hydrogen consumption -- reverse β-oxidation; Carbon dioxide -- Periodicals; Carbon dioxide -- Environmental aspects -- Periodicals; Carbon dioxide mitigation -- Periodicals; Carbon dioxide; Carbon dioxide -- Environmental aspects; Carbon dioxide mitigation; Periodicals; 628.53205
• DOI: 10.1016/j.jcou.2020.101314
• Languages: English
• ISSNs: 2212-9820

Abstract

Highlights: Caproate was produced in a two-stage process. In the first stage SCFAs were produced from three complex substrates. In the second stage CO2 + H2 promoted the production of ethanol. Caproate was produced from SCFAs and ethanol previously accumulated. A CO2 -enriched atmosphere improved the caproate production up to 6 g/L. Abstract: This study describes a two-stage process for the valorization of organic wastes and CO2 /H2 off-gas for the production of short-chain fatty acids (SCFAs) and ethanol, as precursors for n -caproate formation. Three complex organic wastes with previously identified acetogenic members were used to inoculate batch reactors: 1) fibers and 2) leachates from a bagasse fermentation process, and 3) an anaerobic granular sludge from a reactor treating brewery effluents. In the first stage, the reactors loaded with a CO2 /H2 [25:75, v/v] gas mixture produced SCFAs at similar concentrations between 4, 274 and 5, 381 mg/L. In this stage, fiber reactors had the highest H2 consumption. In the second stage, reactors consumed all available H2 and accumulated solvents as well as low concentrations of n -caproate. In particular, sludge reactors produced 3, 528 mg/L of solvents with more than 50% ethanol content, and leachate reactors produced 617 mg/L of n -caproate. By the end of the second stage, in a CO2 -enriched atmosphere, leachate reactors produced 6, 157 mg/L of n -caproate at the expenses of the SCFAs and solvents. Fiber and leachate microbiotas shared autotrophic members and SCFA-elongating bacteria while sludge microbiota differed in composition. This study demonstrated that the use of CO2 /H2 off-gas shifted the composition of SCFAs to a mixture with ethanol which promoted its condensation into n -caproate. A CO2 -enriched atmosphere improved significantly the final production of n -caproate. The results of this study can be used to integrate the n -caproate production, and possibly other medium-chain fatty acids, with biorefinery schemes in which SCFAs and CO2 /H2 off-gases are produced.